Explosive bolt



I March 1, 1966 s. FRANCIS 3,237,521

EXPLOSIVE BOLT Filed Aug. 14, 1963 mmmmumu 38 r 34 I8 42 44 w 48 \\\z%z r"""' 56 46 50 4 INVENTOR. GUS FRANCIS ATTORNEYS United States Patent 3,237,521 EXPLOSIVE BOLT Gus Francis, 1480 S. Josephine, Denver, Colo. Filed Aug. 14, 1963, Ser. No. 302,124 Claims. (Cl. 89-1) This invention relates generally to an explosive bolt; more particularly, it relates to means for fastening walls or bodies together which means can be disintegrated by remote control or otherwise to instantaneously effect separation of the walls or bodies at a desired time.

Among the numerous applications for explosive bolts is that in connection with separation of the stages of multi-stage missiles. For example, after a booster is spent, it is necessary to release it from the missile by indirect control. The most common method of separating two stages of multi-stage missiles has been by the use of metal explosive bolts. These bolts, hollowed out to receive an explosive charge, are used to secure the stages together and upon command the explosive in the bolt is detonated to rupture the bolt and effect separation of the booster and missile.

There are a number of disadvantages associated with the use of conventional explosive bolts, particularly when used in connection with multi-stage missiles for stage separation. The construction and explosive loading of present explosive bolts results in excessive fragmentation when they are exploded with consequent destruction of vital electrical lines, fuel or oxidizer tanks and the possible injury to passengers being carried by the missile.

Explosive bolts are commonly overloaded to insure reliability with the result that upon explosion the resultant excessive explosive force often results in damage to sensitive missile parts through shock. It is possible for the uncontrolled force to be excessive enough to throw the missile off-course in the upper or lower atmosphere or in outer space.

In order to provide redundancy and increased reliability the practice has been to use two charges in one bolt, one on each end, to obtain a double break. Obviously, if explosions occur in both ends of the bolt they must occur simultaneously for satisfactory separation of the parts being held together by the bolt. There are two serious problems associated with the double charge bolt. If one charge only is initiated, the other charge is often initiated by sympathetic detonation resulting from the capability of the metal to transmit the shock wave from the side initiated. This in itself is not particularly harmful; however, the sympathetically detonated charge often goes low order resulting in no break in the bolt. Since it is practically impossible to ignite two bridge wire initiated charges simultaneously with an electric current, one charge is always initiated before the other. Although this time differential of detonation is measured in milliseconds, this is a sufficient delay after the first initiation to permit the shock wave therefrom to set off the other charge low order before it can be initiated by the delayed electrical current.

A second major problem associated with use of a double charge bolt is one of shock wave interference which occurs when both charges happen to detonate substantially simultaneously. The two shock waves are traveling towards each other and their interference often results in preventing one side from breaking or in obtaining breaks where no breaks should occur.

Accordingly, it is an object of this invention to provide an explosive bolt in which fragmentation is reduced to a minimum.

It is another object of this invention to provide an explosive bolt loaded with a minimum amount of explosive to effect destruction thereof so that excessive vibration from detonation of excessive explosive is not imparted to the parts or bodies being separated.

It is a further object of this invention to provide an explosive bolt in which the separation area can be precisely controlled.

It is still another object of this invention to provide an explosive bolt of a double explosive type in which sympathetic detonation of one explosive charge by the detonation of the other charge is eliminated.

It is another object of this invention to provide an explosive bolt as set forth above which is safe, simple in construction, lightweight and can be manufactured by relatively simple manufacturing techniques.

The explosive bolt of the invention, in the single charge modification, comprises an outer surface or case provided with threads and other necessary means for securing two parts together, and a channel or hollow in the middle of the bolt. The separation area of the bolt is defined by a groove. A high explosive charge is positioned in the channel so that it bottoms on a radial plane passing through the groove. An explosive train for building up a detonation wave and detonating the high explosive charge connected to electrical leads leading to the outside of the bolt is provided. As a major inventive feature of the bolt, a shock absorbing and wave focusing or wave directing element in the form of a sleeve of the proper material is mounted around the high explosive charge between it and the periphery of the hollow in the bolt.

In the modification of the explosive bolt in which a double explosive version is used, each end of the bolt is constructed with a channel, a high explosive charge, an explosive train, and a shock absorbing and wave directing sleeve surrounding the explosive charge. A- shock wave distortion plug is located between the explosive charges to break up the shock wave pattern and prevent sympathetic detonation. The plug includes discontinuities and an area having a different density from that of the material from which the plug is made. A groove on either side of the plug defines the two breaking areas and the assembly is so constructed that each high explosive charge bottoms against its corresponding groove. The result of detonation of the high explosive is to effect a tensile stress around each of the grooves causing the bolt to separate from the plug at the grooved areas by a tensile force. The bolt, of course, can be constructed in any suitable manner to fasten together two walls, bodies or other parts which are to be separated, and conventional means remotely controlled or otherwise, can be used to detonate the high explosive through the explosive train.

The invention will now be described in conjunction with the accompanying drawings in which like numerals represent like parts and in which:

FIG. 1 is a partial sectional and schematic view showing two walls joined together by the double explosive modification of the explosive bolt;

FIG. 2 is a partial sectional and schematic view of an explosive bolt using a single explosive;

FIG. 3 is a cross-section of the explosive insert used with the bolt; and

FIG. 4 is a section of the double explosive bolt taken on line 44 of FIG. 1.

Referring to FIG. 1, there is shown two parts 10' and 12 fastened together by a double charge explosive bolt represented generally at 14. The bolt is ordinarily made of steel or other metallic material although other hard materials, such as plastics may be used. The numerals 10 and 12 represent two parts of a structure held together, or appendages, connections, etc. which hold the two parts together .and which when separated permit the parts to separate. The separable elements which separate upon explosion of the explosive bolt or the manner in which they are held together by the bolt, of course, form no part of this invention but the showing of FIG. 1 is merely illustrative of one manner in which two separable parts may be held together by the explosive bolt of this inven tion. A typical application of the invention is the use of the explosive bolt to hold together the booster stages of a missile so that a spent booster may be released by explosion of the bolt.

The explosive bolt 14, in this illustrative application, is provided with a head 16 and threads 18 at the other end, the threads 18 mating with cooperating threads in the part 12 to hold the parts and 12 together. The bolt 14 is provided with two grooves and 22 for a purpose which will be explained later. The shock wave distortion plug 24 or section of the bolt between the grooves may be made integral with the bolt or can be constructed as a separate element joining the bolt sections together in a manner which provides for grooves 20 and 22. The grooves may take any form so long as a reduced diameter area is formed. Plug 24 is provided with bores 26 and 28 for a purpose which will be explained later. The bores are shown as crossed and approximately through the center but their locations are not restricted to these positions. A single bore may be used. The bolt 14 is provided with channels 30 and 32 at either end into which is inserted explosive inserts 34 and 36, respectively, by means of mating threads or inserts and channels as shown. The inserts will be described in detail in connection with FIG. 3. The explosive inserts 34 and 36 are provided with heads 38 and 40, respectively, with hex shapes in this instance to provide for adjustment of the depth of entry of the explosive inserts 34 and 36, respectively, into their respective channels. Inner inserts 42 and 43 are threadably engaged internally of explosive inserts 38 and 40, respectively, for a purpose which will be described later.

It is thus seen that the assembled bolt of FIG. 1 comprises a rod provided with at least two centrally located spaced-apart grooves defining breaking points, the section of the rod between the grooves including at least one area, in this case holes, having a density different than that of the material from which the section is made. A channel is provided in either end of the rod extending from the respective end of the rod substantially to a radial plane intersecting the respective groove. An explosive charge is positioned at the bottom of each channel so that its bottom is substantially on the plane corresponding to that passing through the respective groove and a shock wave absorbing and directing means surrounds each explosive charge. Means are provided for detonating the explosive charge by remote control or otherwise and attaching the bolt to two or more parts to be secured together.

Referring to FIG. 2, there is shown a single charge bolt provided with external threads 18' for use in joining two parts together and including channel 30', explosive insert 34', and inner insert 42'. This modification can be used in the form shown and, of course can be used with a shock wave distortion plug where there is a need to reduce vibration, this latter modification being a single version of the modification of FIG. 1.

Reference is now made to FIG. 3 for a detailed description of the structure of the so-cal-led explosive inserts 34 and 36 of FIG. 1 and 34' of FIG. 2 which are, of course, identical. The numerals used on FIG. 3 correspond to those used in the right hand section of FIG. 1 to indicate identical parts. The explosive insert 34, in the modification shown in FIG. 3, is adjacent a resilient shockabsorbing and shock wave focusing or directing sleeve 44 and is provided with a counter-bored channel 41. The sleeve 44 is constructed with a hollow 46 which is coneshaped in this modification with the apex of the cone facing outwardly, that is, in the direction of the top of the insert. The sleeve 44 is constructed of nylon; however, it is not restricted to this material as other plastic or nonmetallic material having similar physical properties for the absorption of shock waves may be used. Another suitable material is Teflon. It is obvious that a wide range of materials known within the art as having the required properties may be used and suitable material is subject to definition broadly by its function. The element 44 is referred to herein as a shock wave absorbing and directing means or element, the shape of the element being a factor in controlling the path of travel of the shock wave.

The main explosive charge 48 of corresponding shape as the hollow 46 is nested in the hollow, as shown. This material is preferably a high explosive, such as, RDX, PETN, TNT, COMP B, and COMP C. While the shape of the explosive charge 48 is shown as conical, it is not restricted to this design as it could be cylindrical with the same diameter as the base or a column having, for example, only one-fifth of the diameter of the base. The base must have a substantial thickness to insure uniformly applied force. It is preferable that the base be of larger diameter than the top of the column. As is well known, constant velocity in the column is obtained if the L/D (length-to-diameter) ratio of explosive column is 3 or more. For detonating the high explosive, an explosive train is located adjacent the top of the explosive 48 and consists of a charge of lead styphanate 50 adjacent the top of the explosive 48 and adjacent thereto a charge of lead azide 52. A bridge wire (not shown) is used to detonate the lead azide to start the build-up of the detonation wave to detonate the high explosive charge 48. Electrical leads 54 and 56 conduct current from a source outside of the bolt to the bridge wire to detonate the lead azide. A plastic sheath 58 is molded in place to encase the leads inside of inner insert 42 and channel 41. The area above charge 48 mustbe air-tight and this is the purpose of encasing the leads 54 and 56 in hardenable plastic. Another expedient which has been used for making the channel air-tight is to position a cone-shaped metal plug in the channel with the cone facing upwardly and provide the channel with a flange having a hole therein to receive the plug so that when charge 48 is detonated the plug will be forced upwardly into the hole to stop the channel and prevent escape of pressure out through the channel 41. In assembly, the sleeve 44 with the charge 48 mounted therein is preferably first dropped into the channel 30 and final positioning thereof is accomplished by adjustment of insert 34. Insert 34, of course, carries the charges 50 and 52 and the electrical leads. The assembly must be adjusted until the base of charge 48 lies on a radial plane through the approximate center of groove 20. The like explosive charge in the other half of the double charge bolt of FIG. 1 must be likewise adjusted until the face of the explosive lies flush with a radial plane through the center of the other groove 22.

The invention is not limited to the use of a plug like that of plugs 34 and 36 or to the structural arrangement shown and described above, this being merely an illustrative embodiment provided for the proper arrangement of sleeve 44, explosive charge 48, theexplosive train and means for initiating the explosive. It is, however, essential to the invention that the base of the main explosive charge be flush with its corresponding groove and that it be surrounded by the shock absorbing and directing sleeve 44; Any means other than explosive inserts such as those described may be used to properly position the operative elements. The explosive inserts 34 and 36 are merely an illustration of one means by which the operative elements which are essential to the operation of the invention may be properly positioned in the explosive bolt of the invention.

The operation of the invention is as follows: The device of FIG. 1, that is, the double explosive bolt is used to provide redundancy to insure that at least one of the two explosive charges is detonated to provide for separation of the parts 10 and 12 held together thereby. In any arrangement by which two separable parts are held together by the bolt the construction will be such that the parts may separate upon the explosion of only one or both of the charges of the double charge bolt. Upon initiation of the explosion by remote control source, not shown, the explosive train is initiated to build up a detonation Wave to detonate the main explosive charge 48.

It is important that the outer case of the bolt surrounding the sleeve 44 not spall or fragment in any manner whatsoever, the objective being to separate the bolt at the point of the groove. In order to effect separation of the bolt at the groove, the shock wave is cushioned by the sleeve of resilient material 44 and directed toward the bottom of the charge. The sleeve 44 absorbs and minimizes sidewise pressure preventing the mushrooming of the sides of the bolt. The main explosive force is directed toward the base of the charge. This force strikes the base exerting a great tensile force on the bolt body near the groove tending to pull the bolt apart. Failure occurs at the point of greatest weakness, that is, where the side wall abuts the base of explosive charge 48 and the groove on the outside of the metal or, in other words, along a radial plane passing through the groove and adjacent the base of the charge 48. The force occurring is a tensile force and the bolt can be made to separate at any desired tensile strength merely by regulating the size and shape of the explosive charge 48 and the depth of the groove. The bolt breaks clearly at the grooves under the tensile force exerted and there is no fragmentation.

As the energy of the main explosive charge 48 is cushioned and directed toward the base, an efficient use of explosive is effected so that a minimum amount of explosive can be employed. It has been found that the area of the explosive directly against the base directly controls the force applied, that is, once constant velocity is obtained in the explosive column leading to the base chargefonly a small charge is required in the explosive column. A minimum of explosive is then required in the bolt. The advantage of this is that less cushioning is required to prevent spalling of the sides of the bolt than would be required if excess explosives were required.

It is thus seen that the arrangement of explosive charge and sleeve economizes in explosive required by exposing only the main portion of the energy of the explosive to the point at which application is desired. Since a constant velocity is attained in the explosive column, the addition of more explosive in the column is not required, as the column is not required to do useful work, that is, split the sides. The shock absorbing and directing sleeve serves to absorb any excess energy generated and prevents this energy from splitting the sides and thereby creating unwanted explosive forces. The depth of the groove and the dimensions of explosives and sleeve are, of course, related, their relative adjustment being within the skill of the art.

An important feature of the invention, particularly as respects the double explosive bolt for use to provide redundancy, is the feature by which sympathetic detonation of one explosive charge by the detonation of the other explosive charge is prevented. This is accomplished by providing a means near the bottom of the charge for breaking up or distorting the shock wave. A single hole or holes, such as holes 26 and 28 (FIG. 1), are drilled in a section of the bolt referred to herein as a shock wave distortion plug. The holes are preferably drilled substantially perpendicular to the longitudinal axis of the bolt body at a short distance from the base of the charge of high explosive material and directly under the charge. As the force of the explosion is applied to the steel of the plug, a shock wave is immediately formed which moves down the steel and strikes the hole. At this point the shock Wave, being extremely directional, is transferred to the medium in the hole (namely air, or vacuum in outer space). The principal portion of the energy is then lost as the transfer from air or vacuum back to steel is ineflicient. Accordingly, by drilling a hole with a diameter on the order of that of the explosive charge directly under the charge, the main portion of the shock energy is dissipated. The nylon or Teflon sleeve surrounding the unexploded charge tends to also act as a shock absorbing medium to protect that charge from any shock wave energy that is left. When the two charges in the double charge bolt are detonated simultaneously and two waves are generated approaching each other, these waves are so broken up upon reflection from the hole surfaces and by entering a medium of different density from that of the steel in which they are travelling that a complicated shock pattern exists which is not easily amenable to analysis.

The hole pattern in the shock wave dissipation plug or section of the bolt, or the size or shape. of the holes is not critical. Also, the medium in the holes is not limited to air as other materials of different density, preferably less, than the steel of the wave dissipation plug, such as other gases, can be used. Vacuum is suitable as a medium.

It is thus seen that the invention provides an explosive bolt in which the location of the break can be precisely controlled and in which fragmentation is avoided. The bolt provides for an efficient use of explosive so that excess explosive which might rupture the sides of the bolt is avoided. When the bolt is used as a double charge bolt, it is constructed so that there is a minimum of interference between the wave patterns of the two explosions and sympathetic detonation is prevented.

It is therefore to be understood that various modifications and changes may be made in the construction and arrangement of parts of the present invention without departing from the spirit and scope thereof as defined by the appended claims.

What is claimed is:

1. Quick-disconnect connecting means comprising: rod means provided with at least two centrally located grooves defining breaking points of said rod means; the section of said rod means between said grooves including at least one area having a density different than that of the material from which said section is constructed; a channel in either end of said rod means extending from the respective end of the rod means substantially to a radial plane intersecting the respective groove; an explosive means at the bottom of each channel positioned so that its base is substantially on a plane corresponding to that passing through the respective groove, said explosive means being dimensioned so that its circumference along its longitudinal axis does not substantially exceed that of its base at any point; shock wave absorbing and directing means for each of said explosive means positioned between each of said explosive means and the corresponding inner periphery of the corresponding channel, said shock wave absorbing and directing means having an inner surface substantially corresponding to the outer surface of said explosive means; and means for substantially simultaneously detonating said explosive means.

2. The apparatus of claim 1 in which said shock wave absorbing and directing means is made of a material from the class consisting of nylon and Teflon.

3. The apparatus of claim 1 in which the ends of said section are closed and said section is provided with at least one hole.

4. The apparatus of claim 3 in which said hole contains gas.

5-. The apparatus of claim 1 in which the inner periphery of said shock wave absorption and directing means is in the form of a cone.

6. The apparatus of claim 1 in which said explosive means is dimensioned so that its circumference along its longitudinal axis is less than that of its base at any point.

7. Quick-disconnect connecting means comprising: a rod provided with at least two centrally located spacedapart grooves defining breaking points of said rod; a shock wave distortion plug having its ends closed and having at least one hole therein between said grooves; a channel in either end of said rod extending from the respective end of the rod substantially to a radial plane intersecting the respective groove; a cone shaped explosive charge at the bottom of each channel positioned so that its base surface is substantially on a plane corresponding to that passing through the respective groove and the apex of its cone pointing outwardly; a shock wave absorbing and directing sleeve of nylon having a cone shaped interior opening; surrounding said explosive charge with the apex of its cone pointing outwardly; and means for substantially simultaneously detonating said explosive charges.

8. In combination, at least two separable elements adapted to be connected together and an ex losive bolt connecting said elements, said explosive bolt comprising: a rod having a channel therein and a groove defining the breaking point of said bolt; a substantially cone-shaped explosive charge in said channel positioned with its base along a plane substantially corresponding to that passing radially through said groove; a non-metallic sleeve of shock wave absorbing and directing material having a substantially cone-shaped inner periphery surrounding said explosive charge; and means for detonating said explosive charge.

9. In combination at least two separable elements adapted to be connected together and an explosive bolt connecting said elements, said explosive bolt comprising: a rod provided with at least two centrally located spacedapart grooves defining breaking points of said rod; the section of the rod between said grooves including at least one area having a density different than that of the material from which said section is constructed, said section constituting a shock wave distortion means; a channel in either end of said rod extending from the respective end of the rod substantially to a radial plane intersecting the respective groove; a substantially cone-shaped explosive charge at the bottom of each channel positioned so that its base is substantially on a radial plane corresponding to that passing through the respective groove; shock wave absonbing and directing means having a substantially coneshaped inner periphery positioned between each of said explosive charges and the corresponding inner periphery of the corresponding channel; and means for substantially simultaneously detonating said explosive charges.

10. Quick-disconnect fastening means comprising: rod means adapted to connect two objects, said rod means provided with a channel therein; a reduced diameter area in said rod means defining the breaking area of said rod means; explosive means positioned in said channel so that its base is in substantially the same radial plane as said reduced diameter area, said explosive means being formed substantially cone-shaped; shock wave absorbing and directing means formed of a plastic material surrounding said explosive means and positioned between said explosive means and the inner periphery of said channel, said shock wave absorbing and directing means having a coneshaped inner periphery corresponding substantially to the outer surface of said explosive means and positioned with the apex portion of the cone pointing outw ardly; and means for detonating said explosive means.

References Cited by the Examiner UNITED STATES PATENTS 2,653,504 9/1953 Smith 89-1.5 2,679,783 6/1954 Smith 891.5 X 3,087,369 4/1963 Butterfield 89-1 X OTHER REFERENCES Technik, German application 1,098,423, printed I an. 26, 1961.

SAMUEL FEINBERG, Primary Examiner.

BENJAMIN A. BORCHELT, SAMUEL W. ENGLE,

Examiners. 

1. QUICK-DISCONNECT CONNECTING MEANS COMPRISING: ROD MEANS PROVIDED WITH AT LEAST TWO CENTRALLY LOCATED GROOVES DEFINING BREAKING POINTS OF SAID ROD MEANS; THE SECTION OF SAID ROD MEANS BETWEEN SAID GROOVES INCLUDING AT LEAST ONE AREA HAVING A DENSITY DIFFERENT THAN THAT OF THE MATERIAL FROM WHICH SAID SECTION IS CONSTRUCTED; A CHANNEL IN EITHER END OF SAID ROD MEANS EXTENDING FROM THE RESPECTIVE END OF THE ROD MEANS SUBSTANTIALLY TO A RADIAL PLANE INTERSECTING THE RESPECTIVE GROOVE; AN EXPLOSIVE MEANS AT THE BOTTOM OF EACH CHANNEL POSITIONED SO THAT ITS BASE IS SUBSTANTIALLY ON A PLANE CORRESPONDING TO THAT PASSING THROUGH THE RESPECTIVE GROOVE, SAID EXPLOSIVE MEANS BEING DIMENSIONED SO THAT ITS CIRCUMFERENCE ALONG ITS LONGITUDINAL AXIS DOES NOT SUBSTANTIALLY EXCEED THAT OF ITS BASE AT ANY POINT; SHOCK WAVE ABSORBING AND DIRECTING MEANS FOR EACH OF SAID EXPLOSIVE MEANS POSITIONED BETWEEN EACH OF SAID EXPLOSIVE MEANS AND THE CORRESPONDING INNER PERIPHERY OF THE CORRESPONDING CHANNEL, SAID SHOCK WAVE ABSORBING AND DIRECTING MEANS HAVING AN INNER SURFACE SUBSTANTIALLY CORRESPONDING TO THE OUTER SURFACE OF SAID EXPLOSIVE MEANS; AND MEANS SUBSTANTIALLY SIMULTANEOUSLY DETONATING SAID EXPLOSIVE MEANS. 